1. Technical Field
The present technology relates to a pneumatic tire, and particularly relates to a pneumatic tire with enhanced performance on snow and ice at initial use.
2. Related Art
Pneumatic tires known as “studless tires” are known that have enhanced performance on snow and ice such as braking ability on ice and steering stability on snow when traveling on icy and snowy road surfaces. Some studless tires use tread portion compounds including fine protrusions as a filler so as to obtain an edge effect of nipping icy surfaces, and some studless tires use a rubber material including fine voids for the tread portion so as to obtain an edge effect and a water absorption effect.
However, generally, when vulcanizing and curing the rubber, an irregular rubber layer including the filler or the fine voids is not exposed from the tread surface that is in direct contact with the mold, and instead the tread surface is substantially flat. Therefore, at initial use of the tire, the effects of the filler and/or the fine voids may not be sufficiently displayed because the irregular rubber layer formed using the filler and/or the fine voids does not exist on the tread surface.
Conventionally, Japanese Unexamined Patent Application Publication No. 2006-151231A describes a pneumatic tire including a plurality of land portions partitioned by a plurality of main grooves in a tread surface, wherein sub-blocks are formed by dividing the land portions by at least one sipe extending in the tire width direction. On the land portion, a plurality of shallow grooves that is shallower than the sipe and that have a form that is enclosed in the land portion are formed so as to be isolated, that is, so as not to intersect or come in contact with each other. With the pneumatic tire described in Japanese Unexamined Patent Application Publication No. 2006-151231A, the edge effect of the main groove works against relatively large forces, the edge effect of the sipes works against relatively small forces that cause no more than deformation of the land portion, and the edge effect of the shallow grooves works against minute forces.
However, with the pneumatic tire described in Japanese Unexamined Patent Application Publication No. 2006-151231A, the shallow grooves having the form that is enclosed in the land portion are formed so as to be isolated, that is, so as to not intersect or come in contact with the sipe. Therefore, a water path formed by the shallow grooves is closed, and, snow and water discharge performance cannot be enhanced. This leads to the problem of performance on snow and ice not being readily enhanced.